Rebecca J. Eisen, Lars Eisen, Charles B. Beard

Journal of Medical Entomology

Published date January 18, 2016

County-Scale Distribution of Ixodes scapularis and Ixodes pacificus (Acari: Ixodidae) in the Continental United States

  • States that since 1991, when standardized surveillance and reporting began, Lyme disease case counts have increased steadily in number and in geographical distribution in the eastern United States
  • Updates the distribution of I. scapularis and I. pacificus—the primary Lyme disease vectors in the east and western US respectively—from a map published in 1998 to better understand the changing landscape of risk of human exposure
  • Finds the presence of I. scapularis has now been documented from 1,420 (45.7%) of the 3,110 continental United States counties, as compared with 111 (3.6%) counties for I. pacificus
  • Combined, these vectors have been identified in a total of 1,531 (49.2%) counties spread across 43 states—a 44.7% increase in the number of counties that have recorded the presence of these ticks since the previous map was presented in 1998, when 1,058 counties in 41 states reported the ticks to be present
  • Finds the majority of county status changes occurred in the North-Central and Northeastern states, whereas the distribution in the South remained fairly stable
  • Finds that two previously distinct foci for I. scapularis in the Northeast and North-Central states appear to be merging in the Ohio River Valley to form a single contiguous focus
  • Documents a shifting landscape of risk for human exposure to medically important ticks